The term "single-wall domain" refers to a magnetic domain which is movable in a layer of a suitable magnetic material and is encompassed by a single domain wall which closes on itself in the plane of that layer.
Propagation arrangements for moving a domain are designed to produce magnetic fields of a geometry determined by the layer in which a domain is moved. Most materials in which single-wall domains are moved are characterized by a preferred magnetization direction, for all practical pruposes, normal to the plane of the layer. The domain accordingly constitutes a reverse magnetized domain which may be thought of as a dipole oriented transverse, nominally normal to the plane of the layer. Accordingly, the movement of a domain is accomplished by the provision of an attracting magnetic field normal to the layer and at a localized position offset from the position occupied by the domain. A succession of such fields causes successive movement of a domain in a selected direction.
One particularly attractive arrangement for providing the propagation fields is disclosed in A. H. Bobeck U.S. Pat. No. 3,534,347, issued Oct. 13, 1970. That patent describes a pattern of magnetically soft elements coupled to the layer in which domains move. The elements are of a geometry and so disposed to exhibit changing magnetic pole patterns in response to a magnetic field reorienting, typically rotating, in the plane of the layer. Domains follow the changing pole pattern from input to output positions thus realizing shift register operation in response only to the in-plane field--an operation termed "field access."
U.S. Pat. No. 3,618,054, issued Nov. 2, 1971 of P. I. Bonyhard, U. F. Gianola and A. J. Perneski discloses an organization of a domain, field-access arrangement in what is called a "major-minor" mass memory. Magnetically soft elements are arranged to define a plurality of closed "minor loops" which recirculate domain patterns in response to the in-plane field. The minor loops come in close proximity to a "major loop" arranged perpendicular to the axes of the minor loops. Information is transferred between the minor loops and the major loop at transfer positions defined where the loops are most closely spaced.